1. Field of the Invention
The present invention relates to a resistive memory. The invention relates more particularly to a resistive memory including a plurality of reference cells having mutually different resistance values.
2. Description of the Related Art
As resistive memories, there are known an MRAM (Magnetoresistive Random Access Memory), a PRAM (Phase-Change Random Access Memory), and a ReRAM (Resistance Random Access Memory). The feature of the resistive memory is that information is stored by a change in resistance value (resistance state) of a memory element. The resistance state of the memory element is determined by a sense amplifier. Specifically, at a time of an information read-out operation, a read current flowing in the memory element and a reference current flowing in a reference element are compared by a sense amplifier, thereby determining the resistance state of the memory element.
In the conventional resistive memory, however, there is a problem that the read-out characteristics deteriorate due to variance in input offset of the sense amplifier (see, for example, U.S. Pat. No. 6,809,976 or U.S. Pat. No. 6,707,710).